1. Field of the Invention
The present invention relates to a light conductive member, an illuminating device having the light conductive member, and an information processing apparatus having the illuminating device.
2. Related Background Art
For an illuminating device for the reading device of the information processing apparatus such as a facsimile apparatus, an electronic copying machine or the like, there has been employed a discharge tube such as a fluorescent tube or an LED array consisting of a linear array of a multitude of LED chips. Particularly in recent years, the use of the LED array has become popular as the demand for compacter and less expensive products is increasing with the increase of in-home use for example of the facsimile apparatus.
An example of the illuminating device utilizing such LED array will be explained with reference to FIGS. 1A and 1B. In FIG. 1A there are shown an LED array 41, illuminated surface 42 such as a surface of an original, and LED chips 43. FIG. 1A illustrates the schematic configuration of the illuminating device employing the LED array, together with the illuminated surface (original), while FIG. 1B shows an example of illumination intensity distribution on the original surface when the original is illuminated with the illuminating device shown in FIG. 1A.
The illumination intensity distribution on the original surface depends on the number of the LED chips 43 employed, and, if the density of the LED chips 43 is reduced for the purpose of cost reduction, because of the increased interval of the LED chips 43, the illumination intensity distribution on the illuminated surface becomes uneven as shown in FIG. 6B. Consequently it becomes not only impossible to achieve uniform illumination but also there are generated portions which are not illuminated with the sufficient amount of light. As the exact original reading becomes difficult under extremely uneven illumination, there has been a limit in the cost reduction by the decrease of the number of the LED chips.
On the other hand, for a linear illuminating device for expanding the light from a light source in linear shape, there can be conceived a configuration as shown in FIGS. 2A and 2B. In a schematic lateral view and a schematic cross-sectional view respectively in FIGS. 2A and 2B, there are shown a light source 1 such as a halogen lamp, a tungsten lamp or an LED chip, a translucent member 2 with a circular cross section such as a quartz rod, an entrance face 3 of the translucent member 2 for the entry of the light beam from the light source 1, and an area 4 for reflecting or scattering the light, propagating in the translucent member 2, for taking the light out of the translucent member 2. This area 4 is formed, for example, by forming a coarse surface or applying light scattering/reflecting paint on a part of the surface of the translucent member 2.
A reflecting face 5 is provided at an end, opposite to the light source 1, of the translucent member 2, and may be formed by evaporating a metal such as aluminum on an end face of the translucent member 2 itself, or by applying light scattering/reflecting paint, or may be provided as a separate member. The cross-sectional shape of the translucent member 2 is not limited to circular but may also be square or rectangular. FIG. 2C shows the obtained illumination intensity distribution.
As shown in FIG. 2A, the light beam L emitted from the light source 1 and entering the translucent member 2 from the entrance face 3 thereof propagates therein by repeating reflections on the inner face of the translucent member 2, then reflected by the end face opposite to the entrance face 3 upon reaching the above-mentioned opposite face and propagates again in the translucent member 2. When the light enters the area 4 in the course of repeated reflections, the light beam is scattered and a part L1 the light is emitted to the outside through a side opposite to the area 4. The remaining part L2 of the scattered light obliquely enters the exit face thereby being totally reflected thereby and propagates again in the translucent member. Thus, after the repetion of propagation, the light eventually reaching the entrance face 3 is emitted to the outside through the entrance face 3.
In case a light bulb such as a tungsten lamp is employed as the light source 1, the amount of emitted light can be increased by increasing the electric power even despite of the loss of light emitted from the entrance face 3, there can be obtained a reasonably high illumination intensity.
However, such electric light bulb is associated with drawbacks that a high electric power consumption is required for obtaining a high illumination intensity, and that the device cannot be made compact because of the large amount of heat generation. In addition, the service life of the electric bulb is considerably short, even in comparison with that of the fluorescent lamp, necessitating replacements as a result of decrease in the light intensity and filament breakage, so that a maintenance-free device as in the case of LED cannot be obtained.
For these reasons, the illuminating device as the reading light source of the information processing apparatus such as the facsimile apparatus preferably employs an LED light source and has such a configuration as to emit the light therefrom in linear form.
On the other hand, in case an LED is employed as the light source 1, the illumination intensity becomes inevitably low as the light emission amount is less than that of the electric bulb.
For example, in the configuration shown in FIG. 2A, the illumination intensity is high at the side of the light source 1 but is low at the side of the end face opposite to the entrance face 3, thereby providing an extremely uneven illumination.
For resolving this drawback, there is proposed, as shown in a schematic lateral view in FIG. 3A, a method of positioning light sources 1 on both ends of the translucent member 1. As the illumination intensity distribution is compensated by the light beams entering from both ends, the distribution assumes a form as shown in FIG. 3C, which is more uniform than that in FIG. 3B. In this case the cross-sectional configuration is as shown in FIG. 3B and same as that shown in FIG. 2B.
However, even the configuration shown in FIGS. 3A and 3B may still result in the following drawbacks:
(1) As the light sources are positioned longitudinally with the translucent member, the illuminating device becomes longer in comparison with the effective illuminating length of the translucent member;
(2) In case the amounts of light emission of the light sources on both ends are mutually different, the illumination intensity distribution becomes slanted, and the adjustment of the amounts of light emission of both light sources requires an additional cost;
(3) As the device is easily influenced by the longitudinal elongation or contraction of the translucent member, such influence has to be absorbed by the holding structure of the light sources, and, for this reason, it is difficult to achieve satisfactory heat dissipation;
(4) As the electric power supply has to be made to the light sources on both ends, an increased cost is required for the wirings; and
(5) In order to increase the illumination intensity for the entire device, it is necessary, for example, to increase the number of LED chips in the light sources. Such increase requires a corresponding increase of the light entrance face of the translucent member, thus resulting in a larger dimension of the illuminating device and the information processing apparatus.
Also in the color image reading by switching the emission wavelength of the light source and reading the reflected light from the original at each wavelength, the above-mentioned drawbacks (1) to (5) become more serious as the number of signal lines increases for switching the emission wavelength.